Liquid displacement encoder

ABSTRACT

A digitizer is disclosed, wherein the relative change in volume between two fluids is transposed directly into a digital code, in that a pattern of elemental liquid columns in a capillary is displaced relative to a pickup means operating transverse to the capillary. Different arrangements for obtaining higher significant digits as well as doubling the resolution is disclosed.

United States Patent 3,249,724 5/1966 340/173 CH 3,505,872 4/1970 73/362R 1,601,744 10/1926 73/362 3,513,313 5/1970 Schwartz 73/355 PrimaryExaminerMaynard R. Wilbur Assistant Examiner-Jeremiah GlassmanAttorney-Smyth, Roston, & Pavitt ABSTRACT: A digitizer is disclosed,wherein the relative change in volume between two fluids is transposeddirectly into a digital code, in that a pattern of elemental liquidcolumns in a capillary is displaced relative to a pickup means operatingtransverse to the capillary. Different arrangements for obtaining highersignificant digits as well as doubling the resolution is disclosed.

Puke Mape/ LIQUID DISPLACEMENT ENCODER The present invention relates toapparatus for sensing and measuring the displacement of liquid in a tubeand to provide digital representation thereof.

The displacement of a liquid column, particularly of a boundary(meniscus) thereof is usedfrequently to measure fluid expansion andcontraction in representation of pressure and/or temperature. Theacquisition of a digital representation requires usually placement of alarge number of contacts or pickup electrodes along the tube, separatedfrom each other by interelectrode spacing that represents the accuracyor resolution of measurement. Each pickup electrode must pertain to adifferent electric circuit to permit distinctive recognition of theposition of the liquid column in the tube. The entire range of meniscusdisplacement of interest defines the full scale equivalent ofmeasurement along the tube and must be covered by these electrodes.Furthermore, there must be a corresponding number of signal generatingand processing circuits connected individually to these electrodes.Other detecting systems use plural probing beams of radiation across thetube, selectively absorbed by liquid, or the liquid serves as variablediaphragm to obtain an analog readout signal.

The present invention suggests a different and considerably simplerapproach. The basic element of the invention is a capillary whose twoends are subjected to differently expanding and contracting fluids todisplace the content of the capillary. That content is comprised of aplurality of small, elemental liquid columns, separated from each otherby a second plurality of different liquid columns. The two liquids havespecific distinct, detectable characteristics, such as differentelectrical conductivity, different coefficient of absorption of light,generally or for specific wavelength etc. Most importantly, the twoliquids must be immiscible to remain separate. Stationary pickup meansare provided to act across the tubes diameter thereby establishing aparticular deJection range for detecting absence of one or the othertype liquid column in its range. The resulting output represents a digitof low significance for digital representation of the liquiddisplacement in the capillary. The total scale range covered by thedisplacement meter is represented by the total length occupied by thesedifferent type columns.

For practical reasons, one will use two types of liquids to establishthe two sets of interdigitized elemental columns. Consequently, directdigital readout-of liquid displacement in that capillary yields bivalueddigits. However, one could use three or more different liquids toprovide a base-3 or higher number system.

The two ends of the capillary are directly or indirectly ex posed tofluids that may contract or expand into the capillary, independentlyfrom each other, to displace the assembly of elemental columns therein.These fluids on either or both ends of the capillary may be confined toestablish a confined fluid reservoir of predetermined dimensions, to bepart of the system. Alternatively, either or both ends may be subjecteddirectly or indirectly to different, open-end sources of pressure. Theparticular mode of operation will depend upon employment of thecapillary as will be developed more fully below.

For completion of the system it is necessary to establish concurrentlydigital representation of higher significance and to establish a zeroposition for the scale. For example, the number of elemental columns ofthe first liquid type, when passing the pickup means, are counted, afterhaving set the counter to zero with all elemental columns on one side ofthe pickup means or centrally located thereto. The counter should bebidirectional and the pickup means should be constructed to ascertainalso the direction of a displacement in the capillary.

Alternatively, the capillary may be duplicated (or multiplied) with therespective ends subjected to the same fluid pressures or pressuredifferential and displacement action. These additional capillary orcapillaries contain additional elemental liquid columns of differenttypes, but at a greater length. Each additional capillary has also apickup means to ascertain'the position of the respective columnstherein, so as to obtain higher significant digits for the digitalrepresentation. In the simplest form the difierent type columns in thedifferent capillaries are dimensioned and arranged to obtain a binaryscale readout, the columns in the second capillary having twice thelength of the elemental columns in the principal capillary, the columnsin the third capillary having twice the length of the columns in thesecond one, etc. However, the assembly of distinctive columns in allcapillaries occupy the same longitudinal displacement range defining thetotal scale range.

The resolution of the capillary with distinct columns of smallest sizeis per se limited by the requirement of minimum length for the elementalcolumns, depending upon the fluid mechanics in the capillary. Anadditional pair of pickup means, and/or selection of particular phase ofcolumns in additional capillaries can be used to increase, e.g., doubleresolution.

While the specification concludes with claims particularly pointing outand distinctly claiming the subject matter which is regarded as theinvention, it is believed that the invention, the objects and featuresofthe invention and further objects, features and advantages thereofwill be better understood from the following description taken inconnection with the accompanying drawings in which:

FIG. 1 illustrates somewhat schematically a first example of thepreferred embodiment of the present invention;

FIG. la illustrates schematically a particular mode of employment of thecapillary in FIG. 1;

FIG. 2 illustrates a modified example of the preferred embodiment of thepresent invention;

FIG. 2a illustrates a timing diagram of signals developed in theembodiment shown in FIG. 2;

FIG. 2b illustrates a modification of FIG. 2;

FIG 3 illustrates schematically apparatus to adjust the liquid columnsin a capillary;

FIG. 4 illustrates a gravity balanced system in accordance with theprincipal aspects explained with reference to FIG 1;

FIG. 5 illustrates schematically a modified pickup arrangement; and

FIG. 6 illustrates employment of a system as explained for indirectpressure measurement in a protective enclosure.

Proceeding now to the detailed description of the drawings, in FIG. 1thereof is illustrated a first embodiment of the present invention. Afirst basic element or subsystem is shown in the upper part of FIG. 1and in considerable detail. There is first a capillary tube 10 made of,for example, glass or any other material compatible with its content andsubject to requirements related to purpose and function of that content.Elongated tube 10 contains a particular plurality of elemental liquidcolumns 11 of a first liquid, separated from each other by a pluralityof elemental spacer columns 12 of a second liquid.

The elemental columns 11 are similar in size among each other, so arecolumns 12, which are also similar in size to columns 1 1. Of course,tube 10 has uniform internal diameter, so that similarity in size ofthese columns refers to their respective axial dimension, i.e., length.The particular tube 10 established a scaling unit for displacementencoding, and the totallength of space occupied by all of these columnsdefines the total range of the scale. As the length of each elementalcolumn is instrumental in establishing the resolution of the system,they are to be as small as possible.

As a general rule, each of the columns 1 l and 12 must have length atleast 1.5 of the tubes diameter. In other words, the several elementalliquid columns must be at least as large as necessary to preventformation of a droplet causing two columns of the other type to merge.The tube itself is a capillary. The columns 11 do not have to have thesame length as the columns 12, but it is convenient to choose equallength. Particularly, because each of the columns should have minimumlength as the sum of the length of one column 11 and of one column 12defines the scaling unit length as established by this particularsystem. Of course, it may become desirable to increase the margin ofsafety as to minimum length of an elemental column of one type of liquidso that the particular columns are somewhat longer.

The two liquids must be immiscible and must not react with each other.Moreover, they should have additional easily detectable difference in aparticular characteristic. For example, they should have a significantdifference in conductivity, or they should have different radiationabsorption properties. For example, their transmittance of light or oflight of particular wavelength should differ. Presently, in theembodiment of FIG. 1, of a difference in conductance is presumed,requiring, of course, tube to be an insulator.

Neither of the liquids should wet the internal surface of the capillary,at least not significantly, and their surface tension should not differsignificantly, though lengthening of the elemental columns (ordecreasing the diameter of the capillary) may suffice to prevent mergingof two columns of one type liquid around the column that should separatethem. By way of example, one of the liquids, e.g., the one formingcolumns 11 may be mercury, the other liquid may be water, or alcohol,silicone oil or the like.

It may be convenient to call columns 11 the principal elemental scaleunits defining columns, while columns 12 are the spacer columns, thoughthis is basically arbitrary. A unit length displacement is, thus, givenby the length of a column 11 plus the length of a column 12. Assuming,each of them to be of minimum size, about 1% the tubes diameter D, thenthis displacement unit length is the equivalent of about D as volumedisplacement unit. Doubling the resolution will be explained below.

For reasons of simplification, the number of columns 11 is equal to thenumber of columns 12. The total number of pairs of elemental columns, 11and 12, times the length of such a pair defines the total full length ofthe scale covered by the encoding arrangement. Capillary tube 10 must beat least twice that long. Liquid plugs 13 and 14 are provided toseparate the encoder column arrangement from the environment. This,however, is mentioned here only for reasons of completion and may not benecessary in individual cases. Moreover, columns 11 themselves may serveas plugs on each end, with one thereof having equivalent function of aleading marker for establishing zero position of the scale definingcolumns as a whole.

The environment, from which the elemental encoder columns are to beseparated, is defined by the control of tube 10 at the two ends of thecapillary. On one side, tube 10 may terminate in a flask 15, containinga particular fluid 16, that is compressible and/or has a particularcoefficient of thermal expansion, depending upon the employment of theequipment. For many cases, the fluid may be water or silicone oil.However, in many instances, a gas may be required. As can be seen, plugand separation column 14 may be needed in that case.

Assuming the arrangement is to be used as a pressure gauge or meter,fluid 16 as confined in flask 15, provides and establishes reference andbalancing pressure. That may be the function generally of fluid incommunication with the tube 10 on that side, and it is merely a matterof use particulars, whether or not that fluid 16 is in fact confined ina closed system or subject to controlled pressure variation as will bedescribed.

While basically arbitrary, the left-hand side of the capillary may beregarded as being subject to a source of reference pressure in case thearrangement is used as pressure meter. The right-hand end 18 of the tubeis then exposed to the pressure to be measured. As the fluid in flask iscompressed to assume the same pressure as applied to the measuringopening 18 of tube 10, columns 11 and 12 are displaced accordingly, toleft in the drawing. Depending upon the type of fluid that exercisesmeasuring pressure through opening 18, plug 13 may or may not be needed.It can be seen that the liquids constituting columns 11 and 12 should berelatively incompressible. However, it will be appreciated, that therelative volume occupied by columns 11 and 12 in capillary 10 is, or canbe made, to be quite small as compared with the volume of flask 15. Thisway, the relative volume change of the columns 11 and 12 becomesnegligible. Moreover, for example, the columns 11 can be madedissimilar, slightly increasing in length from the left to the right, soas to offset dimension distortion due to relative high pressure whenacting on opening 18.

In case of thermometry, the capillary tube is operated essentially on anoverall isobaric basis as to each end. Flask 15 generally may contain aspecific quantity of fluid that serves as measuring medium, expandingand contracting due to temperature variations at a particular rate;correspondingly a particularly expanding and contracting column of fluid16 extends into tube 10 and shifts the scale defining elemental columnstherein.

Still in case of thermometry, the right-hand end 18 of tube 10 may beopen and may be exposed directly to environmental temperature condition.Alternatively, there may be a second flask 15 (see FIG. 1a) containingsimilar fluid or a difierent one. This way, a differential thermometeris obtained operating on basis of a resulting pressure differential inthe flasks 15 and 15', causing a relative change in volume so that thecolumns 1 1 and 12 are displaced in tube 10 and balance will, thus, berestored in a manner indicative of thermal conditions.

The plurality of alternatingly disposed elemental columns 11 and 12establish a displaceable scale, following the liquid displacement oneither end of the capillary for reasons of temperature and/or pressurechanges of the media acting on the two ends.

The displacement may also be produced by inertia of liquid in flask 15and tube 10 to establish an accelerometer. The column displacement isdetected by and in relation to the position of a pair of probes 20 and21, traversing the wall of tube 10 and facing each other across thecapillary. The probes are preferably made of platinum. The exposedinternal surfaces of probes 20 and 21 are interconnected electrically bya column 11 when disposed in between, the electrodes are in effectdisconnected by a column 12 accordingly. The electrodes establish anelectrical pickup means and their exposed surfaces should be smallerthan the length of each column, particularly smaller than columns 12providing electrical insulation.

Probe 20 is connected to ground or reference potential, probe 21 isconnected to a voltage source B+ via a resistor 22. The polarity of thisbiasing source is immaterial. Thus, probe 21 is high" when electricallydisconnected from probe 20 by a low-conductance column 12, probe 21 islow when connected to probe 20 by a high-conductance column 11. It islikewise immaterial which signal level is counted as a 1" and which is a0. The digital, bivalued output is denoted A.

The length of the scale is defined by the total length of columns 11 and12, which, in turn, defines full scale or total range for themeasurement. When all of the columns 11 and 12 are to the right of theprobes 20-21 (as illustrated), the scale is at one end in relation topickup 20-21. This position is the low-pressure point as to the fluid inflask 15. The other,

high-pressure limit of the scale is reached when all columns 11 and 12are to the left of the probes.

In the specific example, plug 14 may also be an insulating liquid, sothat zero scale value is established by a high" output A. One willchoose this arrangement in case fluid 16 is likewise conductive to someextent, as fluid 16 may have been selected on a different basis; itspressure and/or temperature behavior is more important than itselectrical characteristics. In case fluid 16 is also an insulator, itmay be more advisable to select the first conductive column 11 as zerodefining scale marker.

In the general case, the measuring device has a plurality of columns 11and 12, possibly a rather large plurality of these elemental columnsdefining low-order bivalued digits of the digital, liquid displacementmeasuring device. It is, thus, necessary to provide for high-order bits.This can be done on a cumulative, temporal basis or on aspatial-parallel basis. The latter method is depicted in FIG. 1. Inparticular, there are shown additional tubes 100, 200, 300, for definingdigits of higher significance in and of the digital representationsought to be established.

In particular, the capillary tubes 100, 200 and 300 are provided tocomplete a gray code scale so that the least significant bit value ofthat representation has half the value of the bit value established byscaling tube per se. A different mode of halving the least significantbit value will be explained below with reference to FIG. 2.

Tube 100 has conductive columns 211, 311, respectively, bounded byinsulating spacer columns 212 and 312 to complete the scale length ineach tube. The spacer columns 212 may, in fact, serve as plugs for thisparticular scale length. The several tubes are shown in particular,physical alignment, which aids in the understanding of the invention,but this is not a structural necessity. I

Each tube has a pair of pickup electrodes or probes 120-121, 220-221,320-321. Important is, that the several columns in these tubes aredisposed in particular phase relation to these pickup electrodes for thesame pressure and/or temperature conditions. The tubes 100, 200, 300 arerespectively provided with flasks 115, 215, 315 filled with the sameliquid 16, and the right-hand end of each tube is exposed to the sameenvironment or conditions as is that end of tube 10.

Under these conditions, the phase relation is selected so that in casethe leading edge of the first column 11 is about flush with theelectrodes -21, the first column 111 is displaced for half a columnlength of columns 11 from electrodes 120-121; column 211 is displacedfor a full column length 11 from electrodes 220-221, and column 311 isdisplaced for a full length away from electrodes 320-321, as column 311biparts the full scale length.

The outputs of the electrodes are denoted A, B, C, D. These outputs areapplied to individual pulse shapers 31 to which a digital readout unit30 is connected. These four bits define the column displacement in afour-bit gray code, at a l:l6 full scale resolution. The reason for aunit distance code such as the gray code is that the resolution ishigher by a factor of 2 than the resolution of the scale defined in tube10 per se. Assuming that columns 11 and 12 have the physicallypermissible minimum size of about 1.5 of the tubes diameter D, then theresolution is, in fact, reduced below the tubes diameter. The scale unitof volume displacement is about A D.

The dimensions for the capillaries and columns therein establishingdigits of higher significance have been chosen on basis of similarity ofthe fluids 16 in all flasks. However, in case fluid in the flasks 15,115, 215, 315, is chosen with differing parameters, compressibility orcoefficient of thermal expansion, the dimensions for the elementalcolumns therein must be modified accordingly. Decisive is thatdisplacements remain comparable and that the relations remain constant.

The upper tube 10 in FIG. 2 resembles tube 10 in FIG. 1 and is used toexplain how resolution can be enchanced differently. The tube 10' ispresumed to have the same scale defining columns 11 and 12, and there isalso the pair of electrodes 20-21. However, there is a second pair ofelectrodes 22-23 disposed in the tube displaced from the location ofelectrodes 20-21, by an odd-numbered multiple of half a column length,for example, for 1% column length. Electrode 23 is connected toelectrode 21 (which is connected to ground) while a separate signal canbe derived from electrode 22. That signal is denoted B.

The two electrodes 21 and 22 feed their respective signals to pulseshaping, or squaring, circuits 31A and 31B. Electrodes 21 and 22together read the scale on a modulo-four basis, the unit being definedby half the length of a column (11 and 12) and the sum of the length ofa column 11 and of a column 12 defines the spatial repetition cycle ofthe two-bit code pattern A and B.

FIG. 2a illustrates the output signals A and B as defining a base-4number system for the least significant bits having value equivalent tohalf an elemental column length. Specifically one can see from FIG. 2athat a new f9 ur-bit cycle begins, for example, when A or A -A on B=l. AA represents a scale shift to the left'lcorresponding to increasingmeasuring pressure). A 1A represents correspondingly a scale shift tothe right or pressure decrease. These two different changes aremonitored by detector stages 33 a l 1d 34, respectively responding tosignal ed es A A, A +A. The output of stage 33 is AND gated on to serveas up-counting i nput for a counter 35, the output of stage 34 is ANDgated on B to serve as down-counting input for counter 35 The counter,thus, has state representative of the higher significant digits. Itsrange, of course, represents the full scale length. The stages 33 and 34could be analog-type differentiating stages in case expected liquiddisplacements occur rather fast. However, this cannot be relied upon andpulse edge detection could be carried out digitally, for exan ple, bytemporarily storing the state A l3 and detecting A B, but inhibiting anysuch detection on B T l for up-counting. Downcounting can be carried outand controlled analogously. The pulse shaper circuits 31A and 31B shouldhave artificial hysteresis to prevent multiple counter triggering incase of scale oscillations.

The particular arrangement shown in FIG. 2b is provided to supplementthe displacement gauge of FIG. 2 to provide a different type offormation of digits of higher significance, thus, obviating elements 33,34 and 35.

A pair of bits of higher significance may be produced instead by meansof a second capillary having two sets of pickup electrodes -121 and122-123, which are spaced apart by double the length of an elementalcolumn in tube 10' (Le, by the length of one column 11 plus the lengthof one column 12). There is at least one elemental column 111' incapillary 100 having length of two columns 1 1 plus the length of twocolumns 12. Separation columns 112 are disposed on either side of eachcolumn 1 11'.

A liquid displacement encoder can be made essentially throughappropriate control of filling the capillary with liquid. As fillingrates can be controlled through electrically operated valves in theorder of nanoliters, formation of large numbers of similar sizeelemental liquid columns and particular multiple thereof does notpresent any principal problem.

As shown schematically in FIG. 3, an encoder column assembly afterhaving been placed into a capillary 10, may require particularadjustment relative to the electrodes to establish a zero position.Therefore, the capillary tube 10 (or any of the other type tubes asexplained) is placed between two three-way valves 40 and 41 that canselectively connect one or the other end of tube 10 to a high-pressuresource 43, while the respective other end of tube 10 is connected to alower pressure source 44. Through appropriate manipulation of mastervalves 45 and 46, and upon particular setting of valves 40 and 41, thecolumns are shifted into appropriate position relative to pickupelectrodes 20, 21. In order to facilitate calibration, it may beadvisable to use a first elemental column of the conductive type as azero marker as was mentioned above. For the same reason, a similarminimum size elemental column, such as 11, may be included as zeromarker in each of the various capillaries 100, 100', 200 etc. defininghigher significance digits at larger columns.

The zero position is not necessarily one in which all elemental, scaledefining columns are to one side of the pickup means. Instead, thecenter of the column assembly may the zero position to obtain positiveand negative valued scale readout. It can readily be seen that this ismerely a matter of initial adjustment, placing the column assembly indesired relative position to the pickup means.

In case a liquid displacement encoder of the type described is notnecessarily being disposed in a horizontal position when in use,difference in weight must be considered. Two capillaries, possiblyhaving differently long elemental columns have one end eachinterconnected to form a U-shaped arrangement 50 with a buffer liquid inbetween, for example, of the type used to establish spacer columns. Theother two ends respectively connect to measuring and reference pressuresources. The column assemblies are schematically denoted 51 and 52 andare presumed to be arranged to define two bits of a binary scale. In theillustrated zero position, column assembly 51 is above the pickup means20-21, the column assembly 52 is below pickup means 20, 21. Each columnassembly runs through the scale in different directions.

The embodiments above have been described with electrical readout,whereby the elemental scaling columns and the respectively interspacedelemental spacer column had to have different electrical conductivity,the readout being done on a DC basis. The liquids may differ in in otherrespects. For example, they may have different dielectric constant,whereby an AC bias is applied to the electrodes. A change in impedancerepresents a half unit shift in the capillary.

The two liquids may have different optical properties and, as shown inFIG. 5, a pencil beam 62 of radiation, for example, light is materiallyattenuated by one type of liquid, but transmitted by the other type. Thelight that is permitted to pass enters a photocell 61 providing anappropriate output.

The Free opening of a capillary may not necessarily directly be exposedto the pressure to be measured. This may be particularly so if the fluidis chemically active and corrosive, such as ocean water. In this case,the multiple capillaries with reference pressure flask are immersed in avessel 70, as shown in FIG. 6, having a displaceable, piston-type wall71 or a diaphragm. The interior of that vessel is filled with a liquidor gas 72 compatible with the instrumentation therein and serves aspressure transmitter. That pressure gauging instrumentation may be asshown in FIG. 1 or FIG. 2, directly or as modified in accordance withthe various aspects outlined above.

The inventionis not limited to the embodiments described above but allchanges and modifications thereof not constituting departures from thespirit and scope of the invention are intended to be included.

lclaim:

l. A liquid displacement encoder, comprising:

a capillary tube having first and second ends each exposed to expandingand contracting fluids;

a plurality of first elemental columns of a first liquid in the tubedisposed therein in regular, spaced-apart relationship and occupying aparticular length in the tube equivalent of the scale length of theencoder, there being a first and a last of the columns of the firstplurality respectively closest to the first and second end of the tubebut in physical separation from each of the expanding fluids;

a plurality of elemental columns of a second liquid interposed betweenthe first elemental columns in the tube, the first and second liquidsbeing immiscible and having different particularly detectablecharacteristics, the first and second alternatingly spaced columnstogether establishing the length ofa scale;

pickup means operatively coupled to the tube and effective across thetubes diameter over an area smaller than the length of any of thecolumns to detect absence of a first or of a second column in aparticular location of the tube, the scale as defined by the columns ofthe pluralities having particular scale reference value when in aparticular relative position to the pickup means;

first means connected to the pickup means to derive therefrom digitalrepresentation of low significance of the relative position of theplurality of columns in the tube; and

second means operatively coupled to the first means and likewiseoperating in response to the balance of fluid expansion and contractionto provide digital representation of the relative displacement of highersignificance.

2. A liquid encoder as in claim I, the first columns of liquidhavinilength approximately 1% the diameter of the capillary.

3. liquid encoder as in claim 1, the first and second columns havingsimilar length, each in excess of the diameter of the capillary.

4. A liquid encoder as in claim 1, the pickup means including a pair felectrodes, there being electrical means to bias the electrodes, thefirst and second liquids having different conductivity, the electrodesresponsive to conductance through the capillary across the diameter.

5. A liquid encoder as in claim 1, the pickup means providing aradiation beam across the tube and detecting absorption therein, thefirst and second liquids differing in transmittance of the radiation.

6. A liquid encoder as in claim 3, the pickup means including first andsecond pickup means disposed by an odd-numbered multiple of half acolumn length apart from each other along the tube.

7. A liquid encoder as in claim 1, the second means including countermeans connected to the pickup means and responsive to directionaldisplacement of the columns in the capillary to obtain highersignificant digits.

8. A liquid encoder as in claim 1, the first end merging into a flaskfilled with a particular fluid balancing the position of the columns inthe capillary in their relative position to the second end and to thepickup means.

9. A liquid encoder as in claim 8, the second end of the capillarymerging into a second fluid-filled flask.

10. A liquid encoder as in claim 1, there being means to providecontrolled pressure to the first and second ends of the capillary.

l 1. A liquid encoder as in claim 1, the second means including a secondcapillary having ends exposed to the fluids acting on the firstcapillary, the second capillary having at least one first liquid column,having length which is an integral multiple of the length of the firstcolumn of the first capillary, and having pickup means oriented to thefirst column in the second capillary to establish a phase relationthereto to establish a higher significant digit for the measurementestablished by the relation between pickup means and first columns inthe first capillary.

12. A liquid encoder as in claim 1, including a second capillary havingends exposed to the fluids acting on the first capillary, and includingcolumns of different liquids, there being second pickup means, thecolumns in the second capillary having position relative to the secondpickup means, corresponding to a phase shift as between the columns inthe first capillary and the first pickup means.

1. A liquid displacement encoder, comprising: a capillary tube havingfirst and second ends each exposed to expanding and contracting fluids;a plurality of first elemental columns of a first liquid in the tubedisposed therein in regular, spaced-apart relationship and occupying aparticular length in the tube equivalent of the scale length of theencoder, there being a first and a last of the columns of the firstplurality respectively closest to the first and second end of the tubebut in physical separation from each of the expanding fluids; aplurality of elemental columns of a second liquid interposed between thefirst elemental columns in the tube, the first and second liquids beingimmiscible and having different particularly detectable characteristics,the first and second alternatingly spaced columns together establishingthe length of a scale; pickup means operatively coupled to the tube andeffective across the tube''s diameter over an area smaller than thelength of any of the columns to detect absence of a first or of a secondcolumn in a particular location of the tube, the scale as defined by thecolumns of the pluralities having particular scale reference value whenin a particular relative position to the pickup means; first meansconnected to the pickup means to derive therefrom digital representationof low significance of the Relative position of the plurality of columnsin the tube; and second means operatively coupled to the first means andlikewise operating in response to the balance of fluid expansion andcontraction to provide digital representation of the relativedisplacement of higher significance.
 2. A liquid encoder as in claim 1,the first columns of liquid having length approximately 1 1/2 thediameter of the capillary.
 3. A liquid encoder as in claim 1, the firstand second columns having similar length, each in excess of the diameterof the capillary.
 4. A liquid encoder as in claim 1, the pickup meansincluding a pair f electrodes, there being electrical means to bias theelectrodes, the first and second liquids having different conductivity,the electrodes responsive to conductance through the capillary acrossthe diameter.
 5. A liquid encoder as in claim 1, the pickup meansproviding a radiation beam across the tube and detecting absorptiontherein, the first and second liquids differing in transmittance of theradiation.
 6. A liquid encoder as in claim 3, the pickup means includingfirst and second pickup means disposed by an odd-numbered multiple ofhalf a column length apart from each other along the tube.
 7. A liquidencoder as in claim 1, the second means including counter meansconnected to the pickup means and responsive to directional displacementof the columns in the capillary to obtain higher significant digits. 8.A liquid encoder as in claim 1, the first end merging into a flaskfilled with a particular fluid balancing the position of the columns inthe capillary in their relative position to the second end and to thepickup means.
 9. A liquid encoder as in claim 8, the second end of thecapillary merging into a second fluid-filled flask.
 10. A liquid encoderas in claim 1, there being means to provide controlled pressure to thefirst and second ends of the capillary.
 11. A liquid encoder as in claim1, the second means including a second capillary having ends exposed tothe fluids acting on the first capillary, the second capillary having atleast one first liquid column, having length which is an integralmultiple of the length of the first column of the first capillary, andhaving pickup means oriented to the first column in the second capillaryto establish a phase relation thereto to establish a higher significantdigit for the measurement established by the relation between pickupmeans and first columns in the first capillary.
 12. A liquid encoder asin claim 1, including a second capillary having ends exposed to thefluids acting on the first capillary, and including columns of differentliquids, there being second pickup means, the columns in the secondcapillary having position relative to the second pickup means,corresponding to a phase shift as between the columns in the firstcapillary and the first pickup means.